1. Field of the Invention
This invention relates to a method of transferring a toner image formed on a photoconductive material by an electrophotographic method onto a substrate, and more particularly to an adhesion transfer method using an image receiving sheet having an adhesion layer.
2. Description of the Prior Art
Heretofore, there has been known an electrophotographic copying machine or an electrophotographic printer in which an electrostatic latent image is formed by irradiating a uniformly charged photoconductive material with a light beam which is modulated by an image signal. By use of toner, the electrostatic latent image is developed into a toner image, and then the toner image is transferred to a substrate such as paper.
Various electrophotographic methods have been proposed which are capable of recording continuous tone images with a high degree of reproducibility. For example, in the applicant's Japanese Patent Publication No. 49(1974)-38172 there is disclosed an electrophotographic method, in which a toner image, which has been developed from a latent image formed on a photoconductive material, is transferred to a final substrate by use of an adhesion tape or adhesion sheet. This adhesion sheet is hereinafter referred to as an image receiving sheet. The image receiving sheet is first attached to the toner image, then peeled off and adhered to a final substrate.
A method using a corotron is widely employed to electrostatically transfer a toner image formed on a photoconductive material onto a substrate such as paper. This method, however, is known to be disadvantageous in that it has poor transfer efficiency for the high and low density portions of the toner image. In contrast thereto, the so-called adhesion transfer method, in which the toner image is transferred by use of an image receiving sheet coated by a layer of adhesive material, which layer is hereinafter referred to as the adhesion layer, is advantageous in recording a continuous toner image because its transfer efficiency is extremely high regardless of the image density.
In the conventional adhesion transfer method, an image receiving sheet is generally used, in which the adhesion layer has viscosity and therefore adheres at room temperature. This type of image receiving sheet is used with a release sheet applied thereon, and therefore means for peeling the release sheet off the image receiving sheet before transferring the toner image to said sheet, and means for taking up the peeled off release sheet are needed. Because of inclusion of these means, the apparatus becomes complicated, large and relatively expensive when compared to the apparatus using a corotron.
Further, it is necessary to attach said final substrate, which may be a transparent sheet, onto the adhesion layer after the transfer of the toner image is finished so as not to damage the adhesion layer and so as to prevent the adhesion layer from sticking to fingers or the like. The means for attaching the final substrate, or transparent sheet, to the adhesion layer also contributes to the overall largeness of the system.